1. Field of the Invention
The present invention relates to a field emission display (FED) and fabrication method thereof, and more specifically to a triode-type field emission display (FED) having a grid plate with spacer structure and fabrication method thereof.
2. Description of the Related Art
Field emission display (FED) is a kind of flat panel display attracting intense notice in recent years. The main reason is that it not only has the thin and light characteristics of a liquid crystal display (LCD), but also the high brightness and self emission advantages of cathode ray tube (CRT) displays.
FIG. 1a is a schematic diagram showing the structure of a conventional diode-type (cathode and anode) field emission display. According to the conventional diode-type field emission display 10, the anode electrode 18 provides a high voltage environment to attract electrons emitted from the emission source 12 formed on the cathode electrode 16 of a cathode plate 14, and the electrons impact the phosphor layer 23 on the anode plate 18 resulting in light emission. Since the maximum voltage difference between the cathode electrode 16 and the anode electrode 18 is only 600V, the conventional field emission display has disadvantages of short life span and low brightness.
To overcome the above drawbacks of the diode-type field emission display, a triode type (cathode, anode, and gate electrode) field emission display having high voltage difference has been disclosed. FIG. 1b is a schematic diagram showing the structure of a typical triode-type field emission display.
The main difference from the diode-type field emission display is an additional gate electrode 34. The gate electrode 34 is formed on an insulating layer 36 between the anode electrode 48 and the cathode electrode 40 to control the voltage, resulting in low voltage requirement of electrons emitted from the field emission source 38 of cathode plate 41. The voltage difference 47 between the anode electrode 48 and the cathode electrode 40 is then boosted to 4 KV, and the speed of electrons hitting the phosphor layer 49 formed on the anode plate 46 is increased.
However, in the manufacturing process of conventional gate-controlled triode field emission display 30, complicated and multiple photolithographic and etching steps have to be employed to precisely form the cathode electrode 40 and the gate electrode 34 on predetermined locations of the cathode plate 41 at the same time, and it is extremely difficult to prevent misregistration between the cathode electrode 40 and the gate electrode 34. As a result, the complicated manufacturing process of field emission display reduces throughput and yield.
U.S. Pat. No. 6,380,671 discloses a triode-type field emission display 50. As shown in FIG. 2, a grid plate 53 with a plurality of grid electrodes 55 and through-holes 60 is positioned between the anode plate 52 and the cathode plate 51, and spacers are erected between the grid plate 53 and each of the plates 52 and 54 to maintain a predetermined interval against the atmospheric pressure.
The grid electrodes 55 onto the grid plate 53 enhance the emission of electrons from the emission source 57 and accelerate the electrons passing through-holes 60 in the grid plate 53 to impact the phosphor layers formed on the anode plate 52. Compared with the conventional triode-type field emission display, the grid electrodes 55 are formed on the grid plate rather than on the same plate with cathodes, resulting in simplification of the manufacturing process of the field emission display.
However, since an additional grid plate 53 is positioned between the cathode plate 51 and anode plate 52, different lengths of spacers 62 and 64 have to be erected between the anode plate 52 and the grid plate 53, and between the cathode plate 51 and the grid plate 53 respectively. Due to the essential double spacer attachment processes in the manufacturing process of the field emission display, the number of spacers erected between each two plates is doubled, and the probability of misregistration is increased substantially. Processing time is increased and production is slowed resulting from the additional alignment and attachment processes for increased spacers, particularly in manufacturing process for large display.
While spacers are pre-positioned in desired positions on the grid plate used in another conventional manufacturing process, the additional alignment and attachment processes are performed while spacers are pre-positioned in desired positions on the grid plate. As a result, the manufacturing process still cannot reduce the processing time of spacer positioning and the probability of misregistration.